Cold-gas refrigerator control system



Feb. 25, 1958 H, RNA Em; 2,824,430

COLD-GAS REFRIGERATOR CONTROL SYSTEM Filed Feb. 18,-1955 INVENTORSWILLEM DEN HAAN NIA U LA Q I US VAN WEENEN 2 4 Z 00 Q. AGENT UnitedStates Patent COLD-GAS REFRIGERATOR CONTROL SYSTEM Herre Rinia, Jos JanWillem den Haan, Albert August Bros, and Franciscus Lambertus VanWeenen, Emmasingel, Eindhoven, Netherlands, assignors, by mesneassignments, to North American Philips Company, Inc., New York, N. Y., acorporation of Delaware Application February 18, 1955, Serial No.489,106

Claims priority, application Netherlands February 18, 1954 8 Claims.(Cl. 62-136) This invention relates to a method of operating a coldgasrefrigerator and to a cold-gas refrigerator in which both the startingof the machine is facilitated and the operation of the cold-gasrefrigerator in reverse as a hotgas engine is prevented. Moreparticularly, an auxiliary space is placed in communication with theworking space of the refrigerator when the refrigerator is started orstopped in order that the degree of compression of the cold-gasrefrigerator may be reduced.

The invention concerns a method of operating a coldgas refrigeratorcomprising a first working space of variable volume at a hightemperature and a second space of variable volume at a lowertemperature. These spaces are connected with one another through acooler, a regenerator and a freezer in which the volume of these spacesare varied by piston-like bodies reciprocating with relative phasedifference and having a gas of unvariable chemical compositionperforming a closed thermodynamic cycle in the working space. Such acold-gas refrigerator is often termed a refrigerator operating on thereversed hot-gas reciprocating engine principle. These machines may beconstructed in various ways, for example as a displacer-piston machine,a double-acting machine or a machine in which two cylinders are at anangle to one another. These machines produce low temperatures of forexample 200 C. in one step. When such a machine produces such coldtemperatures in the freezing space, the walls or areas adjacent thisspace will also assume this low temperature. I

During operation a very low temperature of for example 200 C. may,consequently, prevail in the freezer and in the freezing space and amaterially higher temperature of for example +50 C. in the cooler and inthe cooled space. According to the invention it has been found thatafter the refrigerator has been stopped, the machine may startspontaneously operating as an engine owing to the temperature differencebetween the freezing space and the cooled space. The sense of rotationof the machine then reverses, so that then the freezer operates as acooler and the cooling water of the initial cooler performs the functionof a source of heat. The machine then runs until the initially coldparts of the refrigerator have been heated to such an extent and thetemperature difference between the spaces of variable volume has becomeso small, that the machine stops owing to its frictional losses. Duringits operation as an engine the speed may, however, increase to a veryhigh value, so that the normal speed of the machine operating as arefrigerator is exceeded and accidents may result. A further phenomenonis that the starting of the'cold-gas refrigerator may give rise todifiiculties, since therequired starting torque is high and the motorwhich has to supply this torque is often not capable 'to do so.Particularly, if the refrigerator is driven by an electric motor such asa stardelta-connected" electric motor, thetorque supplied by this motorto the refrigerator is often found not to be suflici'ent to start themachine.

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According to the invention a method has been developed by which both thestarting of the machine is facilitated and the operation of the machineas an engine may be avoided.

According to the invention the working space is connected with anauxiliary space, when the refrigerator is started or stopped, so thatthe degree of compression of the machine is reduced.

In one embodiment of the invention it is desirable that the workingspace of the refrigerator during starting should be connected onlyduring a small number of reciprocating movements of the piston-shapedbodies.- The term a small number is to be understood to mean herein thatthe number of revolutions per second may be not more than 100.

The refrigerator suitable for carrying out the afore said method has thefeature that the working space is connected through a duct with theauxiliary space. This duct has a relief valve therein which is open whenthe machine is stopped and closes when the refrigerator is in operation.

The auxiliary space may be constituted by various spaces. In oneembodiment of the invention a working space associated with one cycle ofa cold-gas refrigerator constructed as a multi-cycle machine may beconnected through a duct having a relief valve with a space associatedwith another cycle. Consequently, in this embodiment the working spacesof the machine are connected with one another.

According to a further aspect of the invention the crank case of therefrigerator serves as an auxiliary space. In this case a favorableconstruction may be obtained, if in accordance with a further aspect ofthe invention, the crank case is connected through a duct having atleast one check valve with the working space. This check valve isarranged in a manner such that gaseous medium can flow only from thecrank case to the working space, while the duct has an oil separator forcleaning the oil from the gaseous medium leaving the crank case. Thecrank case is connected with the working space through a second ductwhich has a relief valve capable of disconnecting this secondconnection.

An oil separator may be provided in the first duct connected to theworking space to prevent oil from being deposited in the heatinterchangers when the second duct is connected to the working space. Ina further embodiment of the invention, the second duct from the crankcase to the working space has a by-pass valve which is arranged in amanner such that, when the connection between the working space and thecrank case has been established, working medium can flow only in aselected direction from the working space to the crank case. In thisembodiment the second duct is traversed by medium only from the workingspace to the crank case while the first duct is traversed by medium fromthe crank case to the working space. The first duct, however, comprisesan oil separator by which lubricant is extracted from the medium.

According to a further aspect of the invention additional means areprovided for controlling the operation A structurally simple embodimentis obtained, if the instance is cooled space 11.

relief valve in the communication between the working space and theauxiliary space is subjected to a force which tends to hold this memberin the open position, while provision is additionally made of anelectromagnet which, upon being excited, moves the member against thisforce into the closed position, the electromagnet being excited onlywhen the electric motor is in delta connection.

The invention will be described more fully with reference to oneembodiment thereof in which:

Figure l is a cross-sectional view of a cold-gas refrigerator in whichthe crank case serves as an auxiliary space.

Figure 2 is a schematic view of a star-delta electrical connection.

Thecold-gas refrigerator shown in Figure l is of the displacer-pistontype and comprises a cylinder 1,1in which a displacer-piston 2 and apiston 3 move up and down with a constant phase difference. To this endthe displacer piston is coupled through a connecting-rod system 4 with acrank of a crank shaft 5, while the piston is also coupled by way of aconnecting-rod system 6 with a crank of this crank shaft. Flywheel 30 issecured at one end of crank shaft 5. The space of variable volume 7above the displacer-piston 2 is the freezing space of the machine, thisspace connects a freezer 8, a regenerator 9 and a cooler 10 with acooled space 11 of variable volume between the displacer piston and thepiston. An apertured enclosure 29 surrounding freezer 8 is provided foratmospheric air and condensate is led away through collecting tube 31.Since always a small quantity of working medium will flow away from thecooled or working space 11 of the machine to the crank case or auxiliaryspace 12, a device is provided to convey this lost medium hack to aworking space of the machine, which in this This device comprises aconnecting duct constituted by a duct 13 with a check valve 14, a space15 with an oil separator 16, a duct 17 with a check valve 18 and a duct19. The oil separator 16 is shown only diagrammatically; use may be madeof a conventional oil separator for this purpose. The extracted oilflows through a duct 20, which may be closed by a float 21, to the crankcase of the cold-gas refrigerator. The working space or cooled space 11.of the machine may also be connected through a duct 22, comprising acheck valve, i. e. a relief valve 23 and a check valve 24 with theworking space of the machine. The check valve 24 is arranged in a mannersuch that, if the relief valve 23 leaves the passage of the duct 22open, no medium can flow from the crank case to the working space 11 butit can flow from the working space to the crank case. The relief valve23 is provided with a knob 25, by which it can be manually displaced, ifdesired. The relief valve is held in the open position by a forceexerted by a spring 26. The device comprises inaddilion an electromagnet27, which is excited only when a motor 28, driving the cold-gasrefrigerator, is in delta connection. If the motor is in star connectionor in zero position, the electromagnet is not excited, so that thespring 26 holds the relief valve in the open position. If the magnet isexcited, the relief valve 23 is moved into the closed position againstthe pressure of the spring 26.

The device operates as follows: when the cold-gas refrigerator isstarted, the electric motor 28 is in star connection, so that theelectromagnet 27 is not excited and the relief valve 23 is held in theopen position by the spring 26. Consequently, there is an openconnection between the working space of the machine and the crank case,so that during the instant when the starting torque of the electricmotor is comparatively small, the

medium can flow from the working space of themachine,

to the crank case and need not be compressed. During the period in whichthe pressure in the crank case exceeds that in the working space 11,medium flows from the crankcase through the ducts 13, 17 and 19 to theworking space of the machine, lubricant being extracted from the mediumby means of the oil separator 16. Thus the working space of the machinereceives only oil-free medium, so that it is not contaminated by oil.

If, after a few instants, for example after reciproeating movements persecond of the piston and of the displacer piston, the motor hassulficient speed, it is changed over from star connection into deltaconnection, so that the electromagnet 27 is excited and the relief valve23 is moved into the closed position. From this instant no workingmedium can flow any longer from the working space 11 of the machine tothe crank case, so that the working medium is compressed and thecold-gas refrigerator produces cold.

During the complete period of cold production, the relief valve 23closes the duct 22. If the refrigerator is to be stopped, the electricmotor is changed over from delta connection into zero position by meansof switch A, so that the electromagnet 27 is no longer excited and therelief valve 23 opens the duct 22. Thus, the working space of themachine is connected with the crank case so that the risk of having therefrigerator operate as an engine after the refrigerator has beenstopped is eliminated.

While we have shown and described the preferred embodiment of ourinvention, it will be understood that the latter may be embodiedotherwise than as herein specifically illustrated or described and thatin the illus trated embodiment certain changes in the details ofconstruction and in the arrangement of parts may be made withoutdeparting from the underlying idea or principle of the invention withinthe scope of the appended claims.

What is claimed is:

1. A cold-gas refrigerator comprising cylinder means, at least onepiston mounted for reciprocating movement in said cylinder means, a pairof spaces of variable volume in said cylinder means, a freezer, aregenerator and a cooler in series, an auxiliary space, a duct systemcommunicating at one end with said auxiliary space, and a relief valvelocated in said duct system, said relief valve being operable to connectat least one of said spaces of variable volume to said auxiliary spaceduring relatively low operating speeds of said cold-gas refrigerator.

2. A cold-gas refrigerator comprising a cylinder, a piston and adisplacer mounted for reciprocable movement in said cylinder, a pair ofspaces of variable volume in said cylinder, a freezer, a regenerator anda cooler in series and interconnecting said two spaces of variablevolume, an auxiliary space, a duct system communicating at one end withone of said spaces of variable volume and at the other end with saidauxiliary space, and a relief valve located in said duct system, saidrelief valve being operable to connect said space of variable volume tosaid auxiliary space during relatively low operating speeds of saidcold-gas refrigerator.

3. A cold-gas refrigerator comprising a cylinder, a crank case, ,a crankshaft rotatably mounted in said cylinder, :1 piston and a displacermounted for reciprocable movement in said cylinder, connecting rod meansfor connecting said piston and said displacer to said crank shaft, apair of working spaces of variable volume in said cylinder, a freezer, aregenerator and a cooler connected in series and interconnecting saidtwo spaces of variable volume, a duct system communicating at one endwith one of said spaces of variable volume and at the other end withsaid crank case, and a relief valve located in said duct system, saidrelief valve being operable to connect said two spaces of variablevolume to said crank case during relatively low operating speeds of saidcold-gas refrigerator.

4; A cold-gas refrigerator as set forth in claim 3 further comprising asecond duct system, and at least one check valve being located in saidduct system and directing the flow of medium in a predetermineddirection in said second duct system from said crank case to said oneworking space.

5. A cold-gas refrigerator as claimed in claim 4 in which the resistanceof the duct system, check valve and relief valve to the flow of mediumtherein is less than the resistance of the cooler, regenerator andfreezer to the flow of medium therein at low operating speeds of saidpiston and said displacer.

6. A cold-gas refrigerator as claimed in claim 5 in which said checkvalve is operable to connect said working space to said crank caseonly'when said displacer and said piston have stopped operating.

7. A cold-gas refrigerator as claimed in claim 6 further comprising astar-delta wound electric motor which drives said crank shaft, saidrelief valve being operable to connect said one working space to saidcrank case when said motor is in star connection and being operable todisconnect said one working space from said crank case when said motoris in delta connection and is stopped.

8. A cold-gas refrigerator as claimed in claim 7 further comprising anelectromagnet, a yieldable member urging said electromagnet intooperative engagement with said relief valve, said electromagnet beingconnected to said motor to respond to the delta connection thereofwhereby said electromagnet closes said relief valve against the pressureof said yieldable member.

References Cited in the file of this patent UNITED STATES PATENTS2,011,964 Ajam Aug. 20, 1935 FOREIGN PATENTS 686,239 Great Britain Jan.21, 1953

